As a technology capable of substantially improving frequency usage efficiency, a multiple input multiple output (MIMO) technology for performing radio transmission by using a plurality of transmit and receive antennas is attracting attention and is being put into practical use in a cellular system, a radio LAN system or the like.
A quantity of improvement of the frequency usage efficiency by the MIMO technology is proportional to the number of the transmit and receive antennas. However, the number of the receive antennas which are able to be arranged in a terminal device serving as a reception device is limited. Thus, multi-user MIMO (MU-MIMO) of downlink that a plurality of terminal devices which are connected concurrently are regarded as a virtual large-scale antenna array and transmission signals from a base station device (transmission device) to the terminal devices are subjected to spatial multiplexing is effective for improvement of the frequency usage efficiency.
In the MU-MIMO, the transmission signals addressed to the terminal devices are received by the terminal devices as inter-user-interference (hereinafter, referred to as IUI), so that it is desired to suppress the IUI. For example, in LTE or LTE-Advanced, linear precoding is adopted that a linear filter which is calculated based on channel information notified by each terminal device is multiplied by a transmission signal in advance at a base station device to thereby suppress the IUI.
However, unless orthogonality of channels of the terminal devices which are subjected to spatial multiplexing is high, the IUI is not able to be suppressed effectively, so that there is a limit on the improvement of the frequency usage efficiency in MU-MIMO using the linear precoding (linear MU-MIMO).
Thus, these days, an MU-MIMO technology using non-linear precoding (non-linear MU-MIMO) that non-linear processing is performed on a side of a base station device is attracting attention.
In a case where modulo (residue) operation is possible in a terminal device, it becomes possible to add a perturbation vector with a complex number (perturbation term) obtained by multiplying an arbitrary Gaussian integer by a certain real number as an element to a transmission signal. Thus, by appropriately setting the perturbation vector according to a channel state between the base station device and a plurality of terminal devices to generate a transmission signal, even if the orthogonality of channels of the terminal devices which are subjected to spatial multiplexing is not high, it is possible to substantially reduce desired transmission power and to significantly improve transmission efficiency compared to the linear precoding in which a perturbation vector is not added (NPLs 1 and 2).
However, the non-linear precoding has a problem that in a case where a signal to noise power ratio (SNR) or a carrier to noise power ratio (CNR), a signal to interference plus noise power ratio (SINR) or a carrier to interference plus noise power ratio (CINR) is low, characteristic degradation called modulo-loss is caused that a reception signal point is detected as an erroneous signal point as a result of modulo operation which is performed on a reception side for one received over a border line of the modulo operation due to noise, inter-cell-interference or the like (NPL 3)
Moreover, one error control technology in packet transmission includes an automatic repeat request (ARQ). The ARQ is a scheme in which, in a case where error detection coding, for example, cyclic redundancy check (CRC) coding or the like is added to information data on a transmission side for transmission and an error is detected on a reception side, retransmission of this data is requested to the transmission side. With the ARQ, redundancy of coding is small and high reliability is achieved with relatively simple processing, but retransmission occurs frequently if the error is increased and transmission efficiency is rapidly reduced.
Another error control technology includes (forward) error correction (FEC). The FEC is a scheme in which error correction is performed by applying error correction cording for adding redundancy (parity data) to information data on a transmission side and performing error correction decoding on a reception side.
Further, in a recent radio communication system, a hybrid ARQ (HARQ) scheme in which the ARQ and the FEC are combined is being put into practical use.
In the HARQ scheme, error correction coding is performed and further a packet to which error detection coding is added is transmitted on the transmission side and error detection is performed after error correction decoding on a reception side, and in the case where an error is detected, retransmission is requested to the transmission side. The HARQ is roughly classified into a type-I in which a packet same as a previous one is transmitted at the time of retransmission and combining is performed on the reception side to thereafter perform error correction decoding again and a type-II in which different parity data regarding a previous packet is transmitted at the time of retransmission, and is combined with the previous packet on the reception side to improve redundancy, and then error correction decoding is performed. One example of the type-I includes a chase combining (CC) type and one example of the type-II includes an incremental redundancy (IR) type.